The present invention relates to volume adjustable manual pipettes and, more particularly, to a manually-operated pipette equipped with a quickly settable volume adjustment mechanism and a plunger having damped axial movement.
U.S. Pat. No. 3,827,305 (“the '305 patent”) describes one of the earliest commercially available digitally adjustable air displacement pipettes. To provide for volume adjustment, the pipette includes a threaded shaft extending through a fixed nut. Manual turning of the shaft produces axial movement of a stop member for limiting axial movement of a plunger to define a volume setting for the pipette. The volume setting is displayed on a mechanical micrometer display comprising a series of indicator rings each encircling the threaded shaft.
U.S. Pat. No. 4,909,991 describes a later commercially available single channel manual pipette manufactured by Nichiryo Co. Ltd., Tokyo, Japan. The Nichiryo pipette includes an elongated hand-holdable housing for an upwardly spring biased plunger. An upper end of the plunger extends above a top of the housing and carries a control knob for thumb and finger engagement in manually turning the plunger and for axially moving the plunger in the pipette housing between an upper stop and a lower stop at which all liquid within a tip secured to a lower end of the housing is expelled by the downward movement of the plunger. The upper stop is axially adjustable within the housing in response to a turning of a hollow volume adjustment screw or shaft keyed to the plunger. The axial adjustment of the upper stop adjusts the volume of liquid that the pipette is capable of drawing into the tip in response to upward movement of the plunger to the upper stop. The pipette also includes a lock mechanism including a lock knob for locking the plunger against rotation to thereby set the upper stop in a fixed position and hence set the volume adjustment for the pipette.
For a more complete understanding of the current state of the art relative to the volume adjustability of manual pipettes, each of the above-identified patents is incorporated by reference into this application.
In each of the foregoing prior manual pipettes, volume setting requires the repeated turning of either the threaded volume setting shaft or the turning of the displacement plunger of the pipette while viewing the volume display of the pipette. Where successive volume setting for a pipette are of values of considerable difference, appreciable time and physical effort are required to accomplish the volume settings.
Thus, one of the shortcomings of prior manual pipettes is the time, physical effort and care required to accurately manually set the volume of such pipettes. In an attempt to reduce the time required to change the volume settings of a manual pipette, the Socorex Micropipette Calibra 822 includes a volume setting mechanism including two cylindrical cams. A larger one of the cams shows numbers on a left side of a window of a mechanical volume display for the pipette while a smaller one of the cams shows numbers on a right side of the window. After locking of a plunger-button of the pipette, a turning of a setting wheel turns the larger cam to change the numbers displayed thereby. Then a pulling out of the setting wheel followed by a turning thereof produces a turning of the smaller cam and numbers displayed thereby. Such turning of the cams sets mechanical stops within the pipette to control the volume of liquid, which the pipette will aspirate and dispense. While the volume setting structure of the Calibra pipette may reduce the time required to set the volume of a manual pipette, the volume setting structure is relatively complex and costly when compared to conventional manual pipette volume setting mechanisms as described above. Also, the volume setting provided by the Calibra pipette is not as fine a setting as is provided by conventional volume setting mechanisms.
U.S. Pat. No. 6,428,750 issued Aug. 6, 2002 to the assignee of the present invention (“the '750 patent”), and U.S. Pat. No. 7,175,813 issued Feb. 13, 2007 also to the assignee of the present invention (“the '813 patent”), describe an improved volume adjustable manual pipette having a quick set volume adjustment mechanism and a plunger position sensor. The volume setting of the pipette is monitored by the sensing and control circuitry to provide a real time display of the volume setting of the pipette on the electronic digital display.
In particular, the '813 patent describes a manual handheld pipette capable of being adjusted with both coarse and fine volume setting capabilities, capable of being adjusted by sequentially turning a single volume adjustment member. This pipette has been found to be particularly easy and intuitive to use, as no tools are necessary to make coarse or fine volume adjustments, and only a single control need be handled, as in traditionally adjustable pipettes.
The quick set feature in the '750 and '813 patents referenced above represents a considerable advance in the art of manual pipettes. However, it has been found that when volume settings are advantageously adjusted with small and relatively easy movements, the stability of the volume setting becomes less resistant to drift and more susceptible to bumps and accidental movements.
There is a continuing need for a volume adjustable manually operated pipette including a quickly and easily adjustable volume setting mechanism that remains stable when perturbed. A pipette with a reliable mechanism capable of changing the volume setting relatively rapidly and without unnecessary manipulation would enable enhanced functionality over traditional manually operated pipettes.